I. Field of the Invention
This invention relates
to electrosurgical apparatus and more specifically to bipolar electrosurgical devices for use in intravascular surgery for ablating stenotic deposits adhering to the inner walls of the blood vessel.
II. The use of radio frequency powered instruments for cutting tissue and/or coagulating blood at a bleeding site is well known in the art. For example, reference is made to the Herczog et al U.S. Pat. No. 4,248,231 describing a scalpel having a blade in the form of an insulating substrate on which closely spaced conductive electrodes are affixed. When radio frequency energy of a sufficient potential is applied between the electrodes and the blade is made to cut into tissue, a current flow develops through the tissue bridging the two electrodes resulting in coagulation. In the Stasz U.S. Pat. No. 4,674,498, and entitled "ELECTRO-CAUTERY SURGICAL BLADE", there is disclosed a scalpel arrangement in which the blade also has conductive traces thereon and which are insulated from one another forming a bipolar electrode pair. When RF energy of a predetermined level is applied across the electrodes and the scalpel blade is brought near to the tissue, cutting occurs due to the creation of a arc discharge which creates such high heat energy that the cells comprising the tissue adjacent the instrument desiccate and are severed.
In treating calcified tissue deposits, an rf spark discharge has been used to create a shock wave which, when coupled through a fluid medium to the tissue deposit, results in a breakup thereof (lithotripsy).
II. Discussion of the Prior Art
The buildup of atheromas or the formation of thrombi in a blood vessel can cause serious circulatory problems and when complete blockage occurs, distal tissues may be deprived of oxygen and nutrients, leading to damage or destruction of cell tissue distally of the blockage. As the blockage grows, distal tissue may become more ischemic unless, of course, channelization occurs whereby blood bypasses the constriction. With a narrowed blood vessel, a point may be reached where even a tiny thrombus becomes lodged creating an infarct.
The treatment of diseased blood vessels depends to a large extent on the location of the blockage. In the case of a blocked or partially blocked coronary artery, it has been the practice to perform coronary bypass surgery. In a like fashion, blood vessel shunts have been installed in other body areas as Well. The surgery involved in those procedures tends to be quite traumatic, involving, in the case of coronary-bypass surgery, the opening of the patient's chest and pericardium. In treating deep vein thrombosis or other blockages in the peripheral vasculature, extensive excision and vessel replacement is often required.
More recently, following the technique credited to A. Grunzig, a balloon catheter has been used to restore patency to blood vessels without extensive surgery. In carrying out this technique, a catheter having a small inflatable balloon on its distal end is routed through the vascular system to the site of the restriction to be treated. The deflated balloon is appropriately positioned to span the blockage in question and then a fluid is introduced into the proximal end of the catheter to inflate the balloon to a sufficiently high pressure whereby the blockage is spread open and patency is restored.
As is pointed out in U.S. Pat. No. 4,445,509 to Auth, there are some deficiencies in the Grunzig procedure which renders it ineffective in certain applications. For example, the blockage may be such that it is not possible to safely force the distal tip of the catheter through the blockage prior to the inflation of the balloon. The Auth patent also cites a number of other U.S. patents relating to catheter-mounted cutting devices intended to "tunnel" through a blockage but without doing damage to the healthy blood vessel tissue The invention of the Auth patent is in the design of a rotatably driven cutting tool which will preferentially abrade hard or calcified lesions while not significantly abrading the endothelial lining of the blood vessel.